This invention relates to an improved dye penetrant composition and method for non-destructively testing materials to locate defects open to the surface, such as cracks, and is more particularly concerned with the provision of a dye penetrant containing a single phase red liquid azo dye in concentrated form and which is substantially free of insolubles, and provides brilliant red indications of cracks and voids in a part surface when viewed under ordinary light.
In known penetrant inspection methods for rapid location and evaluation of surface flaws such as cracks in test bodies or parts, a dye penetrant composition containing a liquid vehicle and either a fluorescent or daylight visible dye, and which will penetrate the openings of the surface of cracks or other voids in the part, is applied to the surface of the test body, and the excess penetrant composition is removed from the surface of the body. A developer composition may then be applied to the part surface, which acts as a wick and causes the liquid penetrant containing the dye, which was retained in the cracks, to be drawn up out of the surface defects by capillary action. The part is then exposed to appropriate lighting conditions such as invisible fluorescigenous light or white light, depending on the type of dye used, and the location of the surface cracks is revealed by the emission of fluorescent or visible light by the penetrant dye which was retained in the cracks after the penetrant composition was removed from the surface of the part.
For best efficiency, particularly for the detection and location of minute surface cracks, as well as intermediate size and gross cracks, it is necessary that the dye penetrant composition have high brightness and sensitivity.
There are only a relatively small number of commercially available dyes which can be effectively employed in dye penetrant compositions. The dyes employed, including fluorescent and daylight visible dyes, particularly red visible dyes, are powders which are mixed with the liquid vehicle, which can include surfactants or wetting agents, oils, couplers and extender solvents such as hydrocarbons, e.g. kerosene, light fuel oils, and the like, to produce the dye penetrant formulation. While some fluorescent dyes dissolve relatively well in such liquid vehicles, daylight visible red dyes, or red-visible dyes as termed herein, which are used to a major extent in non-fluorescent formulations, generally do not totally dissolve and even when initially dissolved are subject to precipitation after the mixtures are made. Since red dye penetrants generally have a greater dye content than fluorescent dye penetrants, a serious problem with red penetrants is precipitation of the dye and also deposition of insoluble impurities from the dye in the carrier or solvent.
Accordingly, an object of the present invention is the provision of an improved dye penetrant composition containing dyes which are effective in producing brilliant dye indications from cracks and flaws, but which do not form inactive, undesirable deposits and residues when incorporated into the liquid vehicle of the dye penetrant formulation. A particular object of the invention is the provision of a novel dye penetrant composition containing a highly concentrated liquid single phase red-visible dye composition which immediately and totally enters into solution in the vehicle of the dye penetrant and is essentially free of insolubles, and emits a bright red color. A further object is to provide procedure for dye penetrant inspection of objects, utilizing such dye penetrant composition.